How To: Replace Mechanical Fan with Electric -

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post #1 of 10 Old 02-21-2009, 08:53 AM Thread Starter
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How To: Replace Mechanical Fan with Electric

Alright, I've done a bunch of research on this, and I've yet to come across a writeup for a USDM 97+ XJ, so I'm gonna do one. Let me add that I didn't have any problems with my cooling system, it worked flawlessly, I just wanted to be able to control more cooling at/near idle, without running the A/C. Here's how this thread's going to look:

Part 1: Mechanical Fan removal & Belt re-routing

Part 2: Picking a Fan

Part 3: Installing Electric Fan

Part 4: Wiring

Part 5: Cost Breakdown

***** Part 1: Mechanical Fan Removal & Belt re-routing *****

This is VERY straightforward. There are two small bolts at the top of the fan shroud, and four nuts on the fan clutch. Remove all six, and the fan/shroud with come out the top easily.

Once it's out, you can see that there's only like 2.75" to mount a fan/shroud. It can be done, but the options are slim, especially when trying to get 2000+ CFM. So, the best bet is to remove that fan pulley entirely, since it's now useless. I looked at several other fan installs, and noticed that the pre-97 XJs had an idler pulley next to the thermostat housing. I realized I could use this pulley (mounted on the A/C compressor bracket) to re-route the serpentine belt, eliminating the now useless fan pulley. This is how the belt will look:

Went to the junkyard, and grabbed up this A/C bracket off a '91 for $14:

Using a 4.5" angle grinder, I chopped off the shaft and support for the fan pulley (all this so I had the option to go back to stock, I wasn't sure it was gonna work out right...)

This is how it looks with the modified A/C bracket, and the belt routed (temporarily):

I also bought a spare front alternator bracket, as the new belt would have gone through it, as seen here:

The red lines are the belt outlines, and 1) is the timing cover stud that had to be ground smooth, 2) is the alternator bracket that was modified. It was modified like this:

So that it woulf fit between the top bolt of the alternator bracket and the bolt/nut combo that goes through the bottom of the A/C bracket. Using some lock washers as spacers, it came together perfectly. The A/C bracket bolt hole had to be opened up a bit, but it fits like this:

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post #2 of 10 Old 02-21-2009, 08:54 AM Thread Starter
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This is the final belt clearance. 1) is the belt, 2) the upper half of the alternator bracket, 3) the lower half. Plenty of clearance:

And how much space you now have, note that the upper alternator bracket doesn't stick out past the belt:

***** Part 2: Picking a Fan ******

There are almost endless electric fans to choose from, and there are a few simple parameters you should follow when selecting one:

1) space contraints: you have about 17.5" wide by 11.5" high of radiator core to cool, so a 10" fan is too small, and an 18" fan is too big. 12", 14", and some say a 16" are the best choices

2) CFM: you need to pull (supposedly) around 2000 CFM to keep this motor happy. After I removed my mechanical fan, I used the little 11" auxiliary fan to keep me cool at lights and in traffic, and although the A/C was never on, it did manage to keep me at 210*F. So if you are running the A/C, in traffic, towing, or crawling a lot, you will need more.

3) Amp draw: most fans will draw 20-40 amps on startup, and settle down to 8-12 amps steady state. This usually isn't a deciding factor, unless you're doing a Taurus fan, which is rumored to draw anywhere from 60-90 amps on startup.

4) Here are the most usefull writeups I've found:

Dino Saava - 1800 CFM - 14" -

Marcus (Go Jeep XJ) - 4500 CFM - Taurus Fan -

Maud'Dib (NAXJA) - 4500 CFM - Taurus Fan -

Marcus (Go Jeep XJ) - 2500 CFM - 16" ICE Fan -

Chuck (JC95) - 3300 CFM - 16" Zirgo Fan -

John Wood - 2950 CFM - 16" Perma Cool Fan (bottom of page) -

5) I chose to run a Perma Cool 19114, 14" 2950 CFM fan. It's 3.75" thick (only in a small spot), has an open metal frame, pulls a ton of air, and only draws 30 amp startup/9.5 continuous. It fits great, and should handle any towing/traffic/crawling I can throw at it. The only downside is the $125 price tag:
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post #3 of 10 Old 02-21-2009, 08:54 AM Thread Starter
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***** Part 3: Installing Electric Fan ******

While almost every aftermarket fan comes with the "zip tie & foam pad" mounting system (zip tie the fan to your radiator core), most everyone (including some manufacturers) will recommend you NOT use this on an off-road vehicle, as the flexing of the chassis/radiator core could result in your fan carving a nice hole in the radiator core. Some of the writeups referenced above suggest using the OE fan shroud, which looks like a great option, but I wanted my fan as tight against the radiator as possible, so I made a shroud out of 22 gauge sheet metal. The first step is making a paper template to check clearance:

Once you've got a design that fits well, trace it and cut it out:

I took it to a local fab shop and one of their guys bent up the edges for me:

Then I cut the center out, and test fit it:

After a few minor modifications, I bolted the fan on, and test fitted the whole assembly:

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post #4 of 10 Old 02-21-2009, 08:55 AM Thread Starter
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There's a little over an inch between the bulge in the fan motor and any engine components. I call that a perfect fit:

After a good alcohol bath, I hit it with two coats of Rustoleum, added the fan, threw it in, and re-routed the overflow hose:

** UPDATE **

After wiring this setup, I tested it and was not impressed with it's performance. I had to space the fan out from the radiator core in order to keep it from contacting the hood release bar, and I think this put the fan too far from the core (~1.5"). I ended up removing the upper radiator support, bending the bars on the fan, and mounting it directly to the upper radiator support. I also made some little tabs to mount the bottom two fan brackets. With this setup, the price drops (no $18 sheetmetal) and the fan works better. It looks like this:

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post #5 of 10 Old 02-21-2009, 08:55 AM Thread Starter
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***** Part 4: Wiring *****

I'm powering it using a Radio Shack 40A mechanical relay, 30A fuse (per Perma Cool's instructions), and 10 gauge wire. The fan will be wired in parallel with the OE Auxiliary fan, so that it will be activated by the ECM when either 1) the A/C is turned on, or 2) the engine temp rises above 218*F. I will also have a switch to activate both fans if I choose to (for crawling/idling/towing). I finally found a flawless method of adding a switch and not getting a CEL, for a reasonable price and a bit of work. It will work like this:

NOTE: the diode I used is actually a type 4004, not 4005. And the resistance that I never filled in is a 100 ohm.

I can't take any credit for it, however, as the idea for the DPDT switch came from a member on the All About Circuits forum. Here's the thread:

This is the circuit one of those members suggested. The DPDT switch allows you to easily dupe your ECM:

I got this switch from Radio Shack... not exactly what I wanted, but it fits there, and doesn't have a 'center-off' feature. It works well:

I simply put a hole in the empty slot next to my rear wiper switch:

And it ends up looking like this:

***** Part 5: Cost Breakdown *****

Perma Cool #19114, shipped $137

'91-'96 A/C bracket $15

'91-'01 Alternator bracket $8

New idler pulley $17

Sheet metal, 2' x 2', 22 ga $18 (ended up not using this)

Relays/Wire/fuses $15

Switch/diode/resistor $6


Total $216 ($198 without the sheetmetal)

You could easily have done this cheaper if, for example, you got a smaller fan, or used a Taurus fan, etc. I actually bought a junkyard Taurus fan for $23, but that thing was so huge I didn't even want to mess with it.

Now that both fans operate simultaneously, and the fan is mounted up close to the core, cooling happens almost instantly. If the fans are turned on as the temp is reaching 220*F, it will drop to under 200*F in a matter of 3-4 minutes. I consider this an overwhelming success.
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post #6 of 10 Old 04-05-2010, 06:11 PM
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Today i started replacing my clutch fan for a electric and i took some pictures and i`ll post when i`m done so 2 hour and 2 beers later and the fan/shroud is out and the new A/c bracket witout the fan bearing is step is to make the ford taurus fan(V6 3.8 )fit and do the wiring(i`m electrician so will be easy) just need to do a wiring the best way i can,thank you for the pics help me a lot...cya.
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post #7 of 10 Old 04-05-2010, 06:56 PM
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Nice write up


2000 XJ 4" 33's... TJ on 1 tons and 40's after Afghanistan!

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post #8 of 10 Old 04-05-2010, 08:16 PM
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Nicely done. Thanks for showing good pics of the cut off fan mount - I found it difficult to get pics of this and did not want to pull it back out. If you find that your fan does not push enough air, try a Taurus fan. I did pretty much the same thing except a different fan. My write up is here:

Originally Posted by Motorcharge View Post
So do you actually hear your thoughts in your head or is it just sort of a dull roar before you smash your face into your keyboard and just submit whatever dumb **** ended up on the page?
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post #9 of 10 Old 04-06-2010, 07:06 AM
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Awesome writeup!!!

96 Cherokee Sport w/ 4.0L, AW4, NP231, 4" Rough Country Lift, 31" BFG AT's
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post #10 of 10 Old 04-06-2010, 11:54 AM
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Nice write up and good pics.

Some of your lack of performance from the fan is the lack of a shroud around the outside edge of the fan blades. Right now the fan is just moving air, not really "sucking" air. If you look at basically any OEM fan/housing, the blades are contained with some lip around the outer edge. The fan you bought is really designed to be put into a factory fan shroud but is still somewhat universal (which means it fits nothing).

If you can find a way to put a ring around the fan that seals up to your radiator (like adding it to your sheet metal shroud) I think you will find the performance increase greatly.

Good luck.

2000 Cherokee Classic 4x4, Rusty's 2.5" coils with 3/4" spacers, OME 3" leafs, TnT Track Bar, JKS Lower Arm and Quicker Disco's, Bilstein's, 245/75-16 Dualer REVO's, AJ's Super Rock Rails, Warn Transfer Skid, Factory Front Skid, PORC SYE, swapped D35 for 8.25 with 4.10's and Trac-Loc, removed ABS system and more to come...
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